IGF-I is an insulin-like peptide occurring in the blood and having activity to promote proliferation of various cells, and the production and secretion thereof are dependent on growth hormone.
While IGF-I is a substance in the somatomedin series which mediate the bone growth-promoting effect of growth hormone, it is particularly dependent on growth hormone and, being identified with somatomedin C, it is markedly associated with manifestation of the effect of growth hormone.
Recently, IGF-I has been made available with comparative ease by genetic engineering technology and is known to find application as a therapeutic agent for pituitary dwarfism and a growth promoter for low-height individuals by taking advantage of its growth-promoting activity, as a prophylactic and therapeutic agent for osteoporosis and a therapeutic agent for bone fracture by taking advantage of its chondrocyte proliferating action, as a therapeutic agent for diabetes by taking advantage of its insulin-like activity, and as a therapeutic agent for ulcers, traumas and burns by taking advantage of its protein anabolic action.
However, being a polypeptide of high molecular weight, a dried preparation of IGF-I forms gels on reconstitution to give a non-homogenous solution or undergoes change to a different substance on aging as the result of partial oxidation or deamidation of its polypeptide.
Under the circumstances the inventor of the present invention assiduously attempted to develop a method for preparing a dried composition containing IGF-I which would be highly soluble and have a long shelf-life. As a consequence, the inventor found that a method for preparing a dried composition which comprises drying a solution containing IGF-I together with a strong acid selected from the group consisting of hydrochloric acid, hydrobromic acid, nitric acid, methanesulfonic acid, sulfuric acid, phosphoric acid and oxalic acid is highly soluble and insures long-term stability. This finding and subsequent research led the inventor to the present invention.